The invention relates to a stepping drive mechanism for converting a constant rotatory input motion to a linear movement of given length which first accelerates from zero, then takes place at constant velocity, and finally is decelerated again to zero, in which the constant rotatory input motion introduced into the drive of the apparatus is mechanically transmitted to cylindrical driving cams having indexing grooves provided on their cylindrical circumferential surface, these grooves being engaged by indexing pins provided on a carrier mechanically coupled to the prime mover of the apparatus.
Stepping drives of this kind are used, for example, for driving elongated tables in production lines, for example in transfer lines or packaging machines, where workpieces are moved linearly from one work station to the next in a rapid and vibration-free manner, but also have to be repositioned accurately. For longer linear strokes, stepping drives of the kind mentioned in the beginning have proven useful, in which one indexing pin is provided on a driven carriage for positioning (at the end position) and acceleration, and another is provided for positioning and deceleration, and a plurality of transport indexing pins disposed at equal intervals between the above-mentioned two indexing pins are provided successively in series.
Three cylindrical driving cams disposed coaxially side by side, provided with indexing grooves and driven by electric motors, cooperate with these indexing pins, the indexing grooves cooperating one with the indexing pin for acceleration and positioning, one with the pin for transport at constant velocity, and one with the pin for the deceleration and positioning, in each of the particular phases of linear movement involved. These stepping drives have proven practical and are widely used. On account of their relatively large bulk, depending on the length of the linear movement, difficulties nevertheless occur in using these stepping drives, e.g., for longitudinal table drives between closely adjacent work stations if simultaneously a relatively long linear movement of the order of 3 to 6 m is required, because then the drive mechanism will not fit between the work stations. Further separating the work stations on transfer lines, if it is possible at all, nevertheless requires an enlargement of the overall installation with higher investment costs of ground and factory buildings.